The present invention relates generally to the manufacture of composite reinforcement elements by multidirectional weaving or knitting, and more particularly relates to a lacing needle employed in the final stage of this manufacture.
Various multidirectional weaving or knitting methods are known. In one of the most common methods, a preform is constructed by placing a first series of parallel layers of wires, threads or fibres, on an assembly of detachable rigid rods perpendicular to the latter and interlaced therewith, a second series of layers of wires, threads or fibres perpendicular to the wires, threads of the first series of layers and to said rods and interlaced with the latter, said rods being thereafter driven out and replaced in succession by wires or threads introduced by means of one or more needles in an operation termed "lacing."
For the purpose of carrying out the last-mentioned operation, there are employed needles having an openable eye, for example of the type disclosed in FR-A-2,488,292.
These needles, which may be rectilinear or curved, advantageously comprise at their end in the vicinity of the eye, a blind axial aperture constituting a recess for receiving a spigot provided at the end of each rods. These rods are driven out axially by a thrust exerted by the needle when the latter enters the preform for depositing therein loops of wires or threads forming a third series of layers perpendicular to the first two layers.
When the needle has travelled through the whole of the preform, the rod driven out is released from the needle under the action of its own weight.
This system is particularly advantageous, since the interengagement between each rod and the needle ensures a perfect continuity of their assembly, in particular when the path through the preform is curved.
In its rectilinear or curved path, each needle travels first of all through the preform by driving a rod in front of the needle, then seizes a needleful of wire or thread, then rises through the preform by replacing the rod driven out with the wire or thread. When this replacement has terminated, the needle again descends in the preform through a few centimetres so as to release the needleful of wire or thread (loop release) and recommences a new travel in order to drive out and replace the following rod with a thread loop.
Experience has shown that, when the needle passes downwardly through the interlaced layers of wires, threads or fibres of the perform, the blind aperture of the end of the needle is completely filled with scraps of wires, threads or fibres which become compressed, and this has consequences of three kinds:
The spigot of the rod is unable to enter the aperture of the needle, and escapes right from the start so that the rod is blocked in the preform, which causes deformations and damage to the radial and circumferential wires or threads.
The needle only partly descends the rod which ends up by jamming in the preform, and this causes the same damages and deformations as in the preceding case.
The spigot manages to enter the aperture of the needle but is blocked by being gripped in the latter and the rod is unable to separate from the needle at the end of its downward travel.
In all cases, stoppage of the automatic knitting or weaving cycle occurs, and this requires the intervention of an operator with loss of time and defects in the finished element.
Furthermore, the life span of this finished element is considerably reduced owing to abnormal stresses and its replacement is consequently often necessary.